This study proposes to investigate the structural and metabolic fate of fresh bone autografts and allografts in orthotopic sites when an immediate vascular supply to the bone graft is provided. These functions will be investigated in a canine vascularized fibular replacement model. The allografts will be exchanged between histocompatibility matched animals treated with short term immunosuppression and morphology, metabolic kinetics and mechanical characteristics of the graft studied. The efficiency of the initial vascular supply will be assessed by hydrogen washout techniques and electromagnetic flow methods. Revascularization and bone accretion will be studied by, microangiography and quantitative histologic techniques using in vivo tetracycline labelling and morphometric analysis utilizing image analysis. The metabolic kinetics of the bone graft will be analyzed with regard to resorption and accretion of new tissue utilizing tritiated tetracycline and proline. These results will be correlated with torsional stress testing. The presence of cell mediated and humoral cytotoxic immunity will be investigated after fresh vascularized and nonvascularized bone allografts, and an attempt made ot identify relative differences in host immunization after these two modes of antigen presentation. The physical, histologic and biologic results of this study will be correlated to determine if these parameters are significantly affected by immediate revascularization, immunosuppression and genetic matching.